On This Episode

It’s the space policy guys’ turn to look back at a year that saw great achievements in space. Were they matched by events in Washington DC? Casey and Jason also explore their hopes and fears for 2018. As promised, we also take on the questions and issues submitted by you, our listeners.

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Planetist: 2018/01/08 02:34 CST

As Casey points out, SpaceX has decided against in-orbit assembly for its Mars missions. But most of the mass in orbit for a planetary mission is not hardware but propellant. SpaceX plans on refuelling, with each flight to Mars involving about 5 tanker launches besides the launch of the spacecraft itself.
Even with refuelling, SpaceX wants a huge rocket. But compared to the size of the undertaking, namely sending *many thousands* of people to Mars at each launch window, its rocket is tiny. SpaceX will need launch rates of hundreds per year.
Contrast that with the sorts of things NASA dreams of. NASA's Evolvable Mars Campaign would put perhaps a dozen people on Mars every decade with an average of an SLS launch or two per year. Although current lunar plans are fuzzy, something like the recently discussed Deep Space Gateway would have an even smaller throughput of payload. In comparison with the tasks they might be assigned, NASA's SLS is a far larger rocket than is SpaceX's. Hence, SpaceX's preference for super-heavy lift is not an argument that NASA needs SLS.
To put it another way, the reason Boeing developed the 747 in the late 1960's is that it foresaw demand sufficient to fill many of them every day. The 747 would never had happened had demand been sufficient to fill just one aircraft a week. Is SLS, which seems destined to average a flight a year, at best, really a good idea?
My point is not that SLS is a bad idea, but rather that, as far as I can tell, its desirability has not been established: shouldn't there be a trade study, performed by *engineers*, concluding that SLS is the best way for NASA to go?
The Augustine Committee concluded that a rocket with a capability of about 50 tonnes to LEO would do for NASA, when combined with refueling. With 2 such launch vehicles now in development, is it not high time to consider whether these rockets might get NASA's astronauts NASA's astronauts out into the solar system faster and cheaper than SLS?